Machine tools are used for machining workpieces, such as work pieces of metal, to provide them with the desired shape and configuration, for example, by drilling or boring holes in the workpieces and/or by machining edges to give them a desired, for example, a bevelled, shape. For example, the machining of a connecting rod for connecting the piston to the crankshaft of a reciprocating piston engine involves several different operations which can be performed in one machine tool or sequentially in different machine tools, which can be different or which can have the same basic design but being equipped with different tools, adapted to performing the specific operations. For example, machining this kind of connecting rod can typically include several or all of the following steps:                rough grinding of the surfaces of the blank        rough boring of the pin hole and the crank hole        machining bolt holes and seats        cracking the connecting rod (body and cap) and bolts assembly        finish grinding of the surfaces        milling trapezoid and semifinishing crank hole        finish boring pin hole and crank hole.        
For example, FIGS. 1A-1D show how some of these operations can be carried out on a connecting rod blank 1000 by using different tools 100, 101,102,103 which can be connected to respective spindle heads to be driven by one or more electrical motors, for rotary movement about, for example, a horizontal Z axis (not illustrated in FIG. 1), in a conventional manner. For example, FIG. 1A shows boring of the pin hole with a first tool 100, FIG. 1B shows the machining of bolt holes using a second tool 101, FIG. 1C shows the milling of a trapezoidal end of the blank using a third tool 102, and FIG. 1D shows boring of the crank hole using a fourth tool 103. All of these steps can be carried out by one machine tool, in which the different tools are mounted simultaneously or sequentially. It is, of course, also possible to carry out different steps using different machine tools.
Machines of this type are normally provided with some kind of tool carrier, in which the tools can be replaced depending on the task to be performed by the machine at a certain time or for a certain period. In this specification, the term “tool” is to be interpreted in a generic sense, and can, but must not, include an associated spindle head.
Machine tools for performing machining operations such as drilling and milling, for example, by rotary motion of a tool, for example, for shaping and boring connecting rods for reciprocating piston engines, are well known in the art, and it is thus not considered necessary to describe the operation of a tool drive or of a tool holding mechanism, as the skilled person is aware of how to design this kind of equipment and as appropriate devices are commercially available.
Machine tools are conventionally numerically controlled and in machine tools with rotary tools, machining is performed by producing a controlled relative movement between the workpiece and the corresponding tool. For example, it is known to provide a machine with one or more fixed tools, and to move one or more workpieces, such as a workpiece or blank out of which a connecting rod is to be obtained, in relation to the fixed tool, for example, in parallel with a first horizontal axis (this axis can be the axis around which a tool rotates, or an axis parallel with that axis), in parallel with another horizontal axis perpendicular to the first horizontal axis, and in parallel with a vertical axis.
U.S. Pat. No. 7,442,154 discloses a machine tool comprising a frame in which tools can be mounted in tool carriers, which can be tool spindles. Different tools can be applied at different heights of the frame. A workpiece carrier is provided which can move a workpiece in three different, orthogonal, directions, that is, in a vertical direction and in two perpendicular horizontal directions. The workpiece carrier can also be rotated around a horizontal axis.
Another example of this kind of machine is known from WO-A-2008/089751, which discloses a machine tool based on a reticular frame structure, in which tools can be fixed. The machine tool includes a workpiece carrier which can be displaced along an X-Y-Z guide.
It is observed that when replacing the tools in the machine of U.S. Pat. No. 7,442,154, the operator must access the space within the tool holding frame. Similarly, when replacing the tools in a machine tool as known from WO-A-2008/089751, the operator will need to access the space within the reticular frame. However, this space is limited, inter alia due to the presence of the quill and tools. Similar problems appear to occur when accessing the workpiece carrier for replacing workpieces, or for replacing the workpiece carrier itself, or parts thereof.
WO-2012/156541-A1 discloses a machine tool in which one or more laterally displaceable tool carriers are provided, that can be laterally displaced between an operative position in which they are facing a workpiece carrier so that the workpieces can be machined using the tools carried by the tool carrier, and an inoperative position in which they are not facing the workpiece carrier and in which operations such that change of tools can be carried out easily and comfortably. However, it has been found that a drawback with the solution taught in WO-2012/156541-A1 is that the fixed orientation of the workpiece carrier and the workpieces in relation to the tools implies that in many cases, the machine can only carry out a limited number of operations on the workpieces. It has also been found that it could be desirable to provide an alternative layout, for increased flexibility, for example, when incorporating a machine for machining connecting rods into a system for the manufacture of connecting rods, for example, at the premises of a manufacturer of motor components, motors or vehicles.
EP-1642673-A1 teaches a machine tool in which a plurality of spindles are fixed on a stationary frame structure. A workpiece carrier is arranged to be displaced translationally along different axes, and additionally arranged for rotation so as to position the workpiece in relation to the tools. The structure is simple, but a disadvantage is that the fixed positions of the spindles tend to render the change of tools and maintenance operations rather difficult. Also, the structure of the mechanism for displacing the workpiece carrier is rather complex.
Obviously, many specific machine tool arrangements are known in the art, often for carrying out very specific operations. For example, STADTFELD H. J.: “DIE ZWEITE REVOLUTION IM VERZAHNEN VON KEGELRÄDERN”, WERKSTATT UND BETRIEB, CARL HANSER VERLAG GMBH&CO. KG, DE, vol. 136, no. 6, 1 Jun. 2003, pages 10-14, 16 & 18, ISSN 0043-2792, discloses various machine tool arrangements for the machining of conical gear wheels, with workpiece carriers and tool carriers that are displaceable in relation to each other, the workpiece carrier being arranged to rotate the workpiece around its axis of symmetry.
EP-1201347-A2 discloses a compound machining apparatus with cutting and welding tools, the apparatus including linearly displaceable tool and workpiece carriers, including a rotatably arranged table for the workpiece.
JP-H06-134601-A and DE-202010008327-U1 disclose further examples of machine tools with linearly displaceable tool and workpiece carriers and including means for rotating a workpiece.